1. Field of the Invention
This invention relates to a sterilizable flexible pouch, to a method of using the pouch, and to apparatus which facilitates use of the pouch. More particularly, the invention relates to pouch packages which are steam sterilizable at high temperatures of up to 270.degree. F. and reliably openable, after such steam sterilization, by way of a reliably openable peel seal. Still more particularly, the invention relates to such packages which are sufficiently large and robust to permit steam sterilization of heavy objects, such as a tray bearing medical devices or instruments.
2. Description of Related Art
Various medical instruments and supplies used in hospitals, are subjected to sterilization treatments such as, for example, steam sterilization, ethylene oxide gas sterilization, radiation sterilization, and dry-heating sterilization, before they are used in medical treatments. Ordinarily, the first step in sterilization is to package or wrap the unsterile device before exposing it to a sterilant. Generally, packages are used for sterilization of small, lightweight objects and wrapping is used for sterilization of heavy objects, particularly metal trays in which one or more objects are held. Such trays are usually made of stainless steel and typically weigh from 5 to 16 pounds, and often up to 30 pounds, when loaded.
In all sterilization treatments, there is a general requirement to observe a sterile technique. In the context of packaging or wrapping, it is particularly important that sterile technique be practiced during unwrapping or during opening of a package. For example, sterile technique does not allow a hand or object to contact a sterile item. It is important, therefore, that any flexible wrapping or packaging material have good drapeability such that it will readily fall away from a sterilized item as the item is unwrapped or as a sterilized package is opened.
A current practice of wrapping a tray for sterilization employs a double-layered muslin cloth, commonly known as CSR wrap, that is secured around an unsterile medical device by taping. Normally, a dust cover is also employed in the post-sterilization phase. CSR wrap, however, is prone to fluid strike-though and exhibits tearing with extended use. In addition, sterilization methods employing cloth wrap are normally practiced by first unwrapping the sterilized tray, followed by moving the unwrapped tray to an area where the tray contents will be used. Sterile technique requires careful and precise procedures. Accordingly, cloth wrap practice is time consuming and expensive.
An alternative practice replaces muslin wrap with a disposable non-woven CSR wrap that is applied in the same manner, i.e., double-layering of wrap secured by taping and use of a dust cover. Although non-woven CSR wraps offer both improved fluid resistance and improved bacterial barrier migration over their cloth counterparts, sterilization practices that use these nonwoven materials are still labor intensive and costly.
Steel or plastic self-contained reusable trays fitted with an outer housing that has a replaceable filter have also been employed as sterilization containers. While the steel tray system offers excellent sterility maintenance, it is not an attractive practice for many hospitals because the containers are extremely expensive. Plastic trays, unlike the steel trays, allow for visual inspection and identification of contents by employing a transparent plastic. Although to a lesser degree than the steel counterpart, the plastic self-contained sterilization trays are also expensive. Moreover, sterilization trays have considerable mass which gives rise to a problem of sterilant condensate which arises with this method of sterilization.
Sterilization pouches and bags comprised of paper and plastic webs have found wide applications in hospitals. Plastic webs afford easy identification of contents through a transparent plastic web. However, as mentioned above, these applications have been limited to sterilization of small or lightweight objects that are easily packaged.
Kraft paper, both coated and uncoated, is used in such packages for both steam and gas sterilization but is not well suited for heavy objects. Moreover, opening a sealed paper package gives rise to the generation of loose paper fibers, which is undesirable in an operating room or other area where dust is desirably kept to a minimum.
Non-woven materials have been substituted for paper in such packages. For example, sheets of spun-bonded polyolefin such as "Tyvek" are widely used in packages for gas sterilization. "Tyvek" offers greater drapeability and reduced fluid strike-through as compared to Kraft paper. However, Tyvek will not withstand high temperature steam autoclaving, and is not employed as an alternative to CSR wrap in steam sterilization.
It is obviously important that a sterilizable package be reliably sealed, and that it remain sealed after sterilization such that its sterilized contents remain sterilized for the required time, generally for at least 30 days in the case of hospital instruments. It is also important, however, that the sealed sterilized package is reliably opened without requiring excessive force and without the risk of generating fiber "dust". Peelable heat seals or "peel seals" between opposed plastic webs have been proposed as being suitable for both of these important properties. For example, Sellers, U.S. Pat. No. 3,410,395, discloses a package which comprises a laminar sheet material folded onto itself or assembled with another separately formed sheet or panel and heat sealed to form a pouch. The laminar sheet material comprises a perforated heat sealable film, preferably polyethylene, which is laminated with and bonded to a paper sheet. Steam can penetrate both the paper layer and the perforated film layer to enter the pouch. The heat seal between the facing panels or sheets is said to be peelable and the package is said to be able to withstand steam sterilization and able to be peeled open by the application of a moderate opposing pulling force.
At the present time, the vast majority of steam sterilization of instruments and the like is carried out in hospitals and medical facilities with saturated steam at a temperature of at least 270.degree. F. for a standard three minute cycle. These conditions are referred to hereinafter as "conventional steam sterilization conditions". The packages disclosed by Sellers are incapable of undergoing sterilization at these conventional steam sterilization conditions.
Wilkes, U.S. Pat. No. 4,367,816 discloses a package which is said to be gas sterilizable, and no mention is made of steam. This package comprises a low density polyethylene sheet which is heat sealed to a laminar tear strip made up of a gas-permeable paper sheet bonded to a perforated plastic film, the latter film being a sheet of high density polyethylene coated on both sides with a thin layer of a blend of ethylene vinyl acetate and low density polyethylene. The latter layer is heat sealed to the low density polyethylene sheet to form a peelable heat seal. Again, however, the materials will fail when the package is subjected to conventional steam sterilization conditions at 270.degree. F. A chevron type package is illustrated in FIG. 7.